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1. General Principles & Basic Science MCQs

Practice Set 656 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 13101

Topic: 1. General Principles & Basic Science

What is the primary cellular mechanism of action by which local anesthetics like lidocaine prevent the propagation of action potentials in peripheral nerves?

. Opening voltage-gated potassium channels
. Blocking voltage-gated sodium channels from the intracellular side
. Blocking voltage-gated calcium channels at the presynaptic terminal
. Enhancing inhibitory GABA receptor activity
. Irreversibly inhibiting acetylcholinesterase

Correct Answer & Explanation

. Blocking voltage-gated sodium channels from the intracellular side

Explanation

Local anesthetics diffuse across the axonal membrane in their uncharged form. Once inside, they become ionized and bind to the inner aspect of voltage-gated sodium channels, preventing membrane depolarization.

Question 13102

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely utilized to minimize perioperative blood loss in major orthopedic procedures. By what mechanism does TXA exert its antifibrinolytic effect?
. Inhibiting the release of tissue plasminogen activator (tPA)
. Reversibly binding to lysine receptor sites on plasminogen
. Irreversibly inhibiting cyclooxygenase in platelets
. Directly inhibiting Factor IIa (thrombin)
. Enhancing the activity of antithrombin III

Correct Answer & Explanation

. Reversibly binding to lysine receptor sites on plasminogen

Explanation

TXA is a synthetic analog of lysine. It competitively and reversibly binds to lysine-binding sites on plasminogen, preventing its activation to plasmin and thereby halting fibrin clot degradation.

Question 13103

Topic: 1. General Principles & Basic Science

To minimize radiation exposure to the surgical team during fluoroscopically assisted orthopedic procedures in a lateral projection, where is the optimal position for the surgeon to stand relative to the C-arm?

. On the side of the X-ray source (tube)
. On the side of the image intensifier (detector)
. Directly in front of the X-ray source
. Above the surgical table
. There is no significant difference in scatter between the two sides

Correct Answer & Explanation

. On the side of the image intensifier (detector)

Explanation

The majority of scattered radiation originates from backscatter off the patient toward the X-ray tube. Standing on the side of the image intensifier dramatically reduces the surgeon's radiation exposure.

Question 13104

Topic: Infection, Pharmacology & VTE

The primary challenge in eradicating chronic implant-related osteomyelitis lies in the formation of bacterial biofilms. In the mature phase of a biofilm, what phenotypic shift occurs in the bacterial population?

. Increased metabolic rate and rapid cellular division
. Reversion to a planktonic state susceptible to beta-lactams
. Decreased metabolic activity and phenotypic resistance to antibiotics
. Transition to exclusively anaerobic energy production
. Loss of the extracellular polymeric substance (EPS) matrix

Correct Answer & Explanation

. Decreased metabolic activity and phenotypic resistance to antibiotics

Explanation

Within a mature biofilm, deep-layer bacteria transition into a sessile, metabolically dormant state. This dormancy confers a profound phenotypic resistance to standard antibiotics, which predominantly target actively dividing cells.

Question 13105

Topic: Biomechanics & Biomaterials

A 45-year-old sustains a femur fracture and undergoes Ilizarov external fixation. During the lengthening process, the tension in the transfixing wire gradually decreases over time while the length remains strictly constant. This biomechanical phenomenon is known as:

. Creep
. Stress relaxation
. Fatigue failure
. Hysteresis
. Load sharing

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (tension) over time when a viscoelastic material is held at a constant strain (length). Creep, conversely, is the progressive deformation of a material over time under a constant load.

Question 13106

Topic: Biology, Genetics & Bone Healing

During absolute stability internal fixation of a transverse radius fracture, healing occurs without radiographic callus formation. Which of the following cells is responsible for the leading edge of the cutting cone during this specific healing process?

. Osteoblasts
. Osteocytes
. Osteoclasts
. Chondrocytes
. Fibroblasts

Correct Answer & Explanation

. Osteoclasts

Explanation

Primary bone healing occurs via Haversian remodeling and cutting cones. Osteoclasts form the leading edge to resorb necrotic bone, which is followed closely by osteoblasts laying down new osteoid.

Question 13107

Topic: 1. General Principles & Basic Science

Articular cartilage effectively distributes joint loads and reduces friction. Which zone of articular cartilage contains the highest concentration of water and has collagen fibers oriented parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone has the highest water content and contains Type II collagen fibers arranged parallel to the joint surface. This structural arrangement is critical for resisting shear forces during joint articulation.

Question 13108

Topic: Infection, Pharmacology & VTE
A 70-year-old patient is started on rivaroxaban for DVT prophylaxis following a total knee arthroplasty. Which of the following best describes the specific mechanism of action of this pharmacological agent?
. Direct thrombin inhibition
. Direct Factor Xa inhibition
. Vitamin K antagonism
. Enhancement of antithrombin III activity
. Irreversible cyclooxygenase inhibition

Correct Answer & Explanation

. Direct Factor Xa inhibition

Explanation

Rivaroxaban is an oral direct Factor Xa inhibitor. It effectively prevents the conversion of prothrombin to thrombin without requiring antithrombin III as a necessary cofactor.

Question 13109

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft or graft substitute materials unequivocally possesses osteoconductive, osteoinductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous autograft
. Cortical allograft
. Bone morphogenetic protein-2 (BMP-2)
. Calcium phosphate cement

Correct Answer & Explanation

. Cancellous autograft

Explanation

Cancellous autograft is the gold standard because it provides all three properties: live cells for osteogenesis, growth factors for osteoinduction, and a scaffold for osteoconduction. Products like DBM are osteoinductive and osteoconductive, but lack live cells.

Question 13110

Topic: Biology, Genetics & Bone Healing

A patient with chronic kidney disease presents with diffuse bone pain and osteodystrophy. Laboratory results show hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH). What is the primary biochemical defect causing hypocalcemia in this patient?

. Decreased production of calcitonin
. Excessive urinary calcium loss
. Impaired 1-alpha-hydroxylase activity
. Overproduction of osteoprotegerin
. Primary hyperparathyroidism

Correct Answer & Explanation

. Impaired 1-alpha-hydroxylase activity

Explanation

In chronic kidney disease, the failing kidneys cannot produce 1-alpha-hydroxylase, which is required to convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D. This leads to impaired intestinal calcium absorption and secondary hyperparathyroidism.

Question 13111

Topic: Infection, Pharmacology & VTE

A joint aspiration is performed on a 50-year-old male with an acutely swollen knee. Synovial fluid analysis reveals a white blood cell count of 85,000 cells/mm3 with 90% polymorphonuclear leukocytes. No crystals are seen. What is the most appropriate next step in management?

. Intra-articular corticosteroid injection
. Prescribe oral indomethacin
. Emergent surgical irrigation and debridement
. Initiate allopurinol therapy
. Observation and repeat aspiration in 48 hours

Correct Answer & Explanation

. Emergent surgical irrigation and debridement

Explanation

A synovial WBC count >50,000 cells/mm3 with >75% PMNs is highly diagnostic for septic arthritis. This is an orthopedic emergency requiring immediate surgical irrigation and debridement alongside intravenous antibiotics.

Question 13112

Topic: Surgical Anatomy & Approaches

A 30-year-old man sustains a midshaft humerus fracture resulting from a motor vehicle collision. Upon examination, he demonstrates a weak wrist extension, an inability to extend his metacarpophalangeal joints, and numbness over the dorsal first web space. Which nerve structure is injured?

. Median nerve
. Ulnar nerve
. Radial nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Radial nerve

Explanation

The radial nerve courses intimately along the spiral groove of the midshaft humerus. Injury to it results in wrist drop, inability to extend the fingers, and sensory loss over the dorsal first web space.

Question 13113

Topic: 1. General Principles & Basic Science

When analyzing muscle physiology, slow-twitch (Type I) muscle fibers are highly resistant to fatigue. These fibers rely predominantly on which type of metabolic pathway for energy?

. Anaerobic glycolysis
. Oxidative phosphorylation
. Phosphocreatine breakdown
. Lactic acid fermentation
. Ketone oxidation

Correct Answer & Explanation

. Oxidative phosphorylation

Explanation

Type I (slow-twitch) fibers are dense with capillaries, mitochondria, and myoglobin. They rely on aerobic oxidative phosphorylation to produce ATP, allowing for sustained, fatigue-resistant muscle contractions.

Question 13114

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) is frequently utilized in arthroplasty to secure metallic components to the host bone. By what primary mechanism does PMMA stabilize the orthopedic prosthesis?

. Chemical bonding to hydroxyapatite
. Osteoinduction of the surrounding bone
. Mechanical micro-interlocking with cancellous bone
. Covalent bonding to the metallic implant
. Biological integration with osteoblasts

Correct Answer & Explanation

. Mechanical micro-interlocking with cancellous bone

Explanation

PMMA bone cement acts strictly as a grout, not an adhesive. It stabilizes the implant by mechanical micro-interlocking with the trabeculae of the host cancellous bone and the roughened surface of the prosthesis.

Question 13115

Topic: 1. General Principles & Basic Science

In the early stages of osteoarthritis, one of the first detectable biochemical changes in articular cartilage is a significant increase in water content. This swelling is directly precipitated by which of the following events?

. Increased collagen cross-linking
. Enzymatic loss of proteoglycans
. Hypertrophy of the subchondral bone
. Calcification of the tidemark
. Proliferation of synoviocytes

Correct Answer & Explanation

. Enzymatic loss of proteoglycans

Explanation

The earliest biochemical event in osteoarthritis is the enzymatic degradation and loss of proteoglycans from the extracellular matrix. This uncouples the collagen network, leading to increased cartilage permeability and secondary swelling (increased water content).

Question 13116

Topic: 1. General Principles & Basic Science

According to the Seddon classification of peripheral nerve injuries, which of the following accurately describes an axonotmesis?

. Transient focal demyelination without axonal disruption
. Axonal disruption with preservation of the endoneurium and surrounding connective tissue
. Complete anatomic transection of the nerve trunk
. Loss of vascular supply to the nerve sheath only
. Disruption of the perineurium with an intact axon

Correct Answer & Explanation

. Axonal disruption with preservation of the endoneurium and surrounding connective tissue

Explanation

Axonotmesis involves the physical disruption of the axon and myelin sheath, resulting in distal Wallerian degeneration. However, the supporting connective tissue frameworks (endoneurium, perineurium, epineurium) remain intact, allowing for potential spontaneous recovery.

Question 13117

Topic: 1. General Principles & Basic Science
A patient is admitted and administered unfractionated heparin prior to an emergent orthopedic procedure for an ischemic limb. Which laboratory test is most appropriate to monitor the therapeutic efficacy of this medication?
. Prothrombin time (PT)
. Activated partial thromboplastin time (aPTT)
. Thrombin time (TT)
. Bleeding time
. International normalized ratio (INR)

Correct Answer & Explanation

. Activated partial thromboplastin time (aPTT)

Explanation

Unfractionated heparin binds to antithrombin III, accelerating its inactivation of thrombin and Factor Xa, which primarily affects the intrinsic coagulation pathway. This intrinsic pathway activity is monitored clinically using the aPTT.

Question 13118

Topic: Biology, Genetics & Bone Healing

In the incorporation of a cortical bone allograft, which of the following best describes the physiological process of creeping substitution?

. Osteoblasts synthesize new woven bone prior to any osteoclastic activity.
. Osteoclastic resorption is coupled with simultaneous osteoblastic bone formation.
. Inflammation leads to the direct transformation of fibrous tissue into lamellar bone.
. Complete allograft resorption occurs universally before any new bone formation begins.
. Chondrocytes proliferate and undergo endochondral ossification within the graft.

Correct Answer & Explanation

. Osteoclastic resorption is coupled with simultaneous osteoblastic bone formation.

Explanation

Creeping substitution is the process by which cortical bone grafts are incorporated. It involves osteoclastic resorption through cutting cones followed by osteoblastic bone formation, which can initially weaken the structural integrity of the graft.

Question 13119

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of proteoglycans, the largest diameter collagen fibrils oriented perpendicular to the joint surface, and provides the highest resistance to compressive forces?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest collagen fibrils arranged perpendicular to the joint surface. It has the highest proteoglycan content and the lowest water content, providing maximum resistance to compressive forces.

Question 13120

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is commonly used in total joint arthroplasty to reduce wear. Which of the following is the primary mechanical disadvantage of increasing the cross-linking of UHMWPE?
. Increased adhesive wear
. Decreased fatigue resistance and fracture toughness
. Increased coefficient of friction
. Decreased oxidation resistance
. Increased susceptibility to third-body wear

Correct Answer & Explanation

. Decreased fatigue resistance and fracture toughness

Explanation

While high cross-linking decreases the volumetric wear of UHMWPE, it significantly reduces its mechanical properties, such as fatigue resistance, ductility, and fracture toughness. This increases the risk of mechanical failure or rim fracture.

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